heliotropism

American  

[hee-lee-o-truh-piz-uhm, hee-lee-uh-troh-piz-uhm] / ˌhi liˈɒ trəˌpɪz əm, ˌhi li əˈtroʊ pɪz əm /

noun

1. heliotropic tendency or growth.

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heliotropism British  

/ ˌhiːlɪˈɒtrəˌpɪzəm /

noun

1. the growth of plants or plant parts (esp flowers) in response to the stimulus of sunlight, so that they turn to face the sun

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heliotropism Scientific  

/ hē′lē-ŏt′rə-pĭz′əm /

1. The growth or movement of a fixed organism, especially a plant, toward or away from sunlight. Heliotropism can be easily seen in sunflowers, which slowly turn their large flowers so that they continually face the sun.

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Other Word Forms

• heliotropic
  adjective
• heliotropically
  adverb

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Etymology

Origin of heliotropism

First recorded in 1850–55; helio- + -tropism

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Explanation

Heliotropism is a scientific term for a plant's tendency to turn toward the sun. Sunflowers are well-known for their heliotropism — they move in the sun's direction over the course of a day, tracking it across the sky. Have you ever noticed a house plant growing in the direction of a window? This is an example of heliotropism, when certain plants (and a few other organisms, like fungi) prefer to face the sun and grow in the direction of sunlight. This works with artificial lights as well, and in that case it's known as phototropism. We can trace heliotropism back to the Greek roots helios, "sun," and tropos, "a turn or change."

Example Sentences

See Examples For:

heliotropism

Blocking blue, ultraviolet, red or far-red light with shade boxes had no effect on the heliotropism response.

From Science Daily ● Oct. 31, 2023

The researchers have not yet identified the genes involved in heliotropism.

From Science Daily ● Oct. 31, 2023

In both sets of cases the movement may be modified in a closely analogous manner by geotropism and by heliotropism; though few climbing plants are heliotropic.

From The Power of Movement in Plants by Charles Darwin

Moreover we know from experiments on heliotropism, thermotropism, etc., that even intangible stimuli such as rays of light, etc., impinging unsymmetrically on these delicate cells cause alterations in their behaviour—e.g. arrest or acceleration of growth.

From Disease in Plants by H. Marshall Ward

We thought, at first, that this difference in their positions was in some manner due to heliotropism, for the leaves are highly heliotropic.

From The Power of Movement in Plants by Charles Darwin

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